The origin of the sediment yield of the Ob' and the Yenisei

Abstract:

Introduction:
Nowadays it is nebulous how much matter is delivered by the largest rivers into the Arctic ocean and how much of sediments are eroded by bank and watershed erosion. Thus, these investigations were made for two biggest watersheds of the Arctic Ocean (the Ob' and Yenisei) and their components of sediment budget estimated.

Methods and results:

1.The fieldwork campaign allowed us to obtain characteristic models of the distribution of suspended and bed sediments in the estuaries of the Yenisei and Ob' river
2.The method for estimating the instantaneous sediment yield is developed based on the author's program for extrapolating ADCP measurement data (language R), water velocity and backscatter intensity. The average annual sediment runoff for the Ob' is 63.5 Mt/year, for the Yenisei – 32.5 MT/year;
3.The watershed component of sediment runoff was estimated by the RUSLE, taking into account the trapping of sediments by reservoirs and lakes. For the Ob' potential watershed is 85 MT/year, and 53.6 MT/year for the Yenisei
4.The Bank erosion was calculated based on GSWE, Arctic-DEM, and HYDROATLAS and GRWL databases for the downstream of rivers, which was 35.0 MT/year for the Ob and 21.9 MT/year for the Yenisei.
5.The total deposition of sediments was calculated as a difference between total sediment yield and total erosion in catchments. For the Ob' total deposition was 56.5 MT/year, for the Yenisei is 43 MT/year.

Discussion and conclusion
The sediments deposited in the catchment area or in the bedforms can be eroded again by of snowmelt and rainfall erosion in the catchment area or directly due to the erosion of the banks. The products of erosion gradually move to the end of the river, with the exception of the part of sediment that trapped by reservoirs. For instance, for the Ob', it is only 10% of the watershed erosion, and for the Yenisei, it is 17% of eroded soil on the catchment. According to the calculations, bank erosion for both downstream is less than the watershed component of sediment runoff. The fact that these components are comparable and it gives some progress in solving the still unexplored question of the role of the bank and watershed components in the origin of sediment runoff of large rivers.

Acknowledgments
This work powered by the grant №18-05-60219 of Russian Foundation for Basic Research(RFBR)